EMBRYOLOGICAL INVESTIGATIONS 257 



common English frog, Rana temporaria, and in the 

 closely allied Rana esculenta y the branchial blood- 

 vessels develop in very different manner, although 

 ultimately reaching the same condition. 



But the most remarkable series of facts with 

 regard to variation in the later stages of develop- 

 ment is afforded by the recently published observa- 

 tions of Professor Brooks and Mr. Herrick on the 

 metamorphoses of certain small decapod Crustacea 

 of the genus Alpheus. These are essentially 

 tropical forms, not unlike small crayfish in appear- 

 ance, and about an inch or so in length. They are 

 brilliantly coloured and occur most abundantly 

 in shallow water, more especially amongst coral 

 reefs. A few species live freely, but the majority 

 are found inhabiting the tubes of sponges, or dwell- 

 ing in holes and crannies in the porous coral lime- 

 stone. The development of thirteen species was 

 carefully studied by Messrs. Brooks and Herrick, 

 and the remarkable conclusion was arrived at that 

 " individuals of a single species sometimes differ 

 more from each other as regards their metamor- 

 phoses than do the individuals of two very distinct 

 species." It is not merely that different individuals 

 hatch at different stages of development : one indi- 

 vidual may appear with characters, e.g., the number 

 and form of the legs, which occur at no stage in 

 the development of other individuals of the same 

 species. In some cases the differences in develop- 

 mental history were associated with differences in 

 the locality from which the specimens were obtained. 

 Thus individuals of a given species observed at 



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